SI4736-C40 Datasheet, PDF (21/42 Pages) Silicon Laboratories – BROADCAST AM/FM RADIO RECEIVER

Si4736/37/38/39-C40
5.3. FM Receiver
The Si4736/37/38/39 FM receiver is based on the
proven Si4700/01 FM tuner. The receiver uses a digital
low-IF architecture allowing the elimination of external
components and factory adjustments. The
Si4736/37/38/39 integrates a low noise amplifier (LNA)
supporting the worldwide FM broadcast band (64 to 108
MHz). An AGC circuit controls the gain of the LNA to
optimize sensitivity and rejection of strong interferers.
An image-reject mixer downconverts the RF signal to
low-IF. The quadrature mixer output is amplified,
filtered, and digitized with high resolution analog-to-
digital converters (ADCs). This advanced architecture
allows the Si4736/37/38/39 to perform channel
selection, FM demodulation, and stereo audio
processing to achieve superior performance compared
to traditional analog architectures.
5.4. AM Receiver
The highly-integrated Si4736/37/38/39 supports
worldwide AM band reception from 520 to 1710 kHz
using a digital low-IF architecture with a minimum
number of external components and no manual
alignment required. This digital low-IF architecture
allows for high-precision filtering offering excellent
selectivity and SNR with minimum variation across the
AM band. The DSP also provides adjustable channel
step sizes in 1 kHz increments, AM demodulation, soft
mute, seven different channel bandwidth filters, and
additional features, such as a programmable automatic
volume control (AVC) maximum gain allowing users to
adjust the level of background noise. Similar to the FM
receiver, the integrated LNA and AGC optimize
sensitivity and rejection of strong interferers allowing
better reception of weak stations.
The Si4736/37/38/39 provides highly-accurate digital
AM tuning without factory adjustments. To offer
maximum flexibility, the receiver supports a wide range
of ferrite loop sticks from 180–450 µH. An air loop
antenna is supported by using a transformer to increase
the effective inductance from the air loop. Using a 1:5
turn ratio inductor, the inductance is increased by 25
times and easily supports all typical AM air loop
antennas which generally vary between 10 and 20 µH.
5.5. Weather Band Receiver
The Si4736/37/38/39 supports weather band reception
from 162.4 to 162.55 MHz. The highly integrated
Si4736/37/38/39 meets NOAA specification, receives all
seven NOAA specified frequencies, implements narrow-
band FM de-emphasis, and supports 1050 Hz alert tone
detection. In addition, the Si4736/37/38/39 provides
advanced features not available on conventional radios,
such as an AFC and a dynamic channel bandwidth filter.
The AFC locks on to the strongest signal within a
narrow, adjustable frequency range to compensate for
any potential frequency errors such as crystal tolerance
or transmit frequency errors. The AFC ensures the
channel filter is always centered on the desired channel
providing optimal reception. The dynamic channel
bandwidth feature utilizes a wide filter in strong signal
conditions to provide best sound quality and a narrower
filter in weak conditions to provide best sensitivity.
5.6. Digital Audio Interface
(Si4737/39 Only)
The digital audio interface operates in slave mode and
supports three different audio data formats:
 I²S
 Left-Justified
 DSP Mode
5.6.1. Audio Data Formats
In I²S mode, by default the MSB is captured on the
second rising edge of DCLK following each DFS
transition. The remaining bits of the word are sent in
order, down to the LSB. The left channel is transferred
first when the DFS is low, and the right channel is
transferred when the DFS is high.
In Left-Justified mode, by default the MSB is captured
on the first rising edge of DCLK following each DFS
transition. The remaining bits of the word are sent in
order, down to the LSB. The left channel is transferred
first when the DFS is high, and the right channel is
transferred when the DFS is low.
In DSP mode, the DFS becomes a pulse with a width of
1DCLK period. The left channel is transferred first,
followed right away by the right channel. There are two
options in transferring the digital audio data in DSP
mode: the MSB of the left channel can be transferred on
the first rising edge of DCLK following the DFS pulse or
on the second rising edge.
In all audio formats, depending on the word size, DCLK
frequency and sample rates, there may be unused
DCLK cycles after the LSB of each word before the next
DFS transition and MSB of the next word. In addition, if
preferred, the user can configure the MSB to be
captured on the falling edge of DCLK via properties.
The number of audio bits can be configured for 8, 16,
20, or 24 bits.
5.6.2. Audio Sample Rates
The device supports a number of industry-standard
sampling rates including 32, 40, 44.1, and 48 kHz. The
digital audio interface enables low-power operation by
eliminating the need for redundant DACs on the audio
baseband processor.
Rev. 1.0
21